In the field of power electronics such as a motor driver, a switching power supply, and the like, a gate driver circuit for driving a power transistor is a very important element technology. In the present disclosure, a combination of a power transistor such as a half-bridge circuit, an H-bridge circuit, a single-phase inverter, a three-phase inverter, a switching power supply, or the like, and a driver circuit for driving the power transistor will be generally referred to as a switching circuit.
FIG. 1 is a simplified block diagram of a switching circuit. A switching circuit 100R includes a half-bridge circuit 102 and a gate driver circuit 200, and supplies a load connected to an OUT terminal with a rectangular AC voltage VOUT that transitions to two voltages VDD and VSS.
The half-bridge circuit 102 includes a high-side transistor 104 and a low-side transistor 106, which are power transistors.
The gate driver circuit 200 includes a high-side driver 210 and a low-side driver 220. The high-side driver 210 includes a first current source 212 for sourcing a current to a gate of the high-side transistor 104 in an enable state and a second current source 214 for sinking a current from the gate of the high-side transistor 104 in the enable state.
When a control signal SH is at an ON level (e.g., high) for instructing to turn on the high-side transistor 104, the first current source 212 is enabled and the second current source 214 is disabled. Thus, a current ION is supplied from the first current source 212 to the gate of the high-side transistor 104 to raise a gate voltage VGH, and when it exceeds a threshold value, the high-side transistor 104 is turned on.
When the control signal SH is at an OFF level (e.g., low) for instructing to turn off the high-side transistor 104, the first current source 212 is disabled and the second current source 214 is enabled. Thus, the charge on the gate of the high-side transistor 104 is discharged by a current IOFF generated by the second current source 214 to decrease the gate voltage VGH, and when it falls below the threshold value, the high-side transistor 104 is turned off.
The low-side driver 220 includes a first current source 222 and a second current source 224, and is configured in a similar manner to the high-side driver 210.
When the high-side transistor 104 and the low-side transistor 106 are externally attached to the gate driver circuit 200, there may be a case where it is desired to adjust the amounts of the currents ION and IOFF according to a required slew rate (slope) of gate capacitance and gate voltage of the high-side transistor 104 and the low-side transistor 106.